Experimental Investigation of Cenosphere Epoxy Syntactic Foam Composites

Abstract

Polymer matrix composites provide lower weight structures and result in improved efficiency and performance in transportation applications. Thermosetting polymers when used with suitable hollow reinforcing constituents, higher specific properties can be achieved that cater to variety of applications. Development of syntactic foams with cenospheres serves dual purpose of beneficial utilization of industrial waste fly ash and reduction in the component cost in addition to weight reduction. In the present study, LAPOX L-12 epoxy resin is used as the matrix material and fly ash cenospheres (hollow microspheres) in as received and silane modified conditions are used as filler. Manual stirring method is employed for developing cenosphere/epoxy syntactic foams with as received and surface treated cenospheres in 20, 40 and 60 volume %. With increasing cenosphere content, density of untreated and silane treated foams decreases. Influence of cenosphere surface treatment and volume fraction of cenospheres in epoxy matrix on compression, quasi-static compression, flexural, tensile, dynamic mechanical analysis, wear and erosion properties are investigated in this work. Effect of arctic conditions on the compressive and flexural response of cenosphere/epoxy syntactic foams is dealt to understand the behavior of foams under extreme conditions. Samples are conditioned under arctic environment at a temperature of -60°C. Compression and flexural tests are then conducted at room temperature as well as at in-situ -60°C on the conditioned samples and compared against unconditioned samples tested at room temperature. For the case of unconditioned samples, compressive strength decreased whereas compressive modulus increased with increasing cenosphere volume fraction for both surface modified and as received cenospheres. For the arctic conditioned samples, a reduction in compressive modulus and significant increase in strength is observed for untreated and treated syntactic foams as compared to their unconditioned counterparts. Increase in flexural modulus is noted while a decrease in flexural strength is observed as compared to neat resin at room temperature with increasing filler content for both untreated and treated cenosphere reinforced syntactic foams. For the case of arcticexposed samples, an apparent increase in flexural modulus is observed as compared to room temperature tested cenospheres/epoxy syntactic foams. In addition, an apparent increase in the flexural strength is noted under arctic environment. Room temperature quasi-static compressive response is investigated at different strain rates. The energy absorption of syntactic foams increases with increase in cenosphere content. Compressive modulus of untreated and treated syntactic foams is observed to be higher than that of neat epoxy sample at the same strain rate. Silane treated foams exhibit higher modulus. Yield strength of untreated and treated foams decreases as compared to neat epoxy. Tensile modulus of both untreated and treated syntactic foams increases with increase in cenosphere volume fraction as compared to neat epoxy. Strength values of syntactic foams show decreasing trend as compared to neat epoxy. Treated syntactic foams registered better results as compared to untreated ones. Storage modulus increases with increasing cenosphere content and decreases with increasing temperature. Loss modulus of syntactic register lower values as compared to neat epoxy, while damping is noted to be increasing. Syntactic foams with treated cenospheres reveal higher values of damping for all the volume fractions. Treated syntactic foams render higher stiffness and damping as compared to untreated syntactic foams and neat epoxy at elevated temperatures. Wear rate decreases with increasing cenosphere content at all the tested conditions. Specific wear rate decreases significantly with increasing applied loads. Further, coefficient of friction decreases with higher filler loading and filler surface modifications. Wear debris is analysed further and disc temperature is also reported. Erosion behavior is studied at room temperature for 30 to 90° impact angles and 30 to 60 m/s velocities. Results show a strong dependence of impact angle and velocity on erosion rate of syntactic foams. With increasing cenosphere content erosion rate decreases for all impact angles. Erosion rate decreases with increasing impact angle and with decreasing velocity. Structure-property correlations of all the investigated properties are presented with the help of exhaustive SEM images to understand underlying mechanisms. Finally, the potential of using the evaluated properties are presented in the form of property map. These property maps provide guidelines toindustrial practioners and researchers in selecting appropriate materials based on the envisaged applications.